Mobile communication system, base station apparatus and mobile station apparatus

ABSTRACT

To prevent a collision from occurring at the time of random access in cases such as handover, response to paging and the like where a mobile station apparatus performs random access in response to directions from a base station apparatus. In a mobile communication system in which a mobile station apparatus  200  uses a signature of a beforehand determined signature group at the time of random access with a base station apparatus  100 , the signature group is comprised of a signature group managed by the base station apparatus  100  and another signature group managed by the mobile station apparatus  200 . The signature group managed by the base station apparatus  100  includes signatures associated with particular random access reasons to be selected by the base station apparatus  100.

TECHNICAL FIELD

The present invention relates to a mobile communication system, basestation apparatus and mobile station apparatus using a cellular wirelessscheme.

BACKGROUND ART

Currently, in 3GPP (3rd Generation Partnership Project), the W-CDMAsystem has been standardized as a 3rd cellular mobile communicationsystem, and its service has been started sequentially. Further, HSDPA(High Speed Downlink Packet Access) with the communication speed furtherincreased has also been standardized, and its service is being started.

Meanwhile, in 3GPP, evolution in 3rd Generation Radio Access (EvolvedUniversal Terrestrial Radio Access: hereinafter, referred to as “EUTRA”)has been studied. As downlink in the EUTRA, an OFDM (OrthogonalFrequency Division Multiplexing) system is proposed. Further, proposedas uplink in the EUTRA is a DFT (Discrete Fourier Transform)-spread OFDMtype single carrier communication system.

As shown in FIG. 14, the uplink of EUTRA is formed of an uplink pilotchannel UPiCH, random access channel RACH, and uplink scheduling channelUSCH (for example, see Non-Patent Document 1).

The uplink random access channel RACH of E-UTRA contains anon-synchronized random access channel and synchronized random accesschannel. Herein, a band of 1.25 MHz is used as a maximum unit of thenon-synchronized random access channel. Then, for example, as shown inFIG. 15, a plurality of channels for access is prepared, and configuredto be able to respond to a number of accesses.

Among intended purposes of the non-synchronized random access channel,it is the biggest purpose to synchronize a mobile station apparatus(hereinafter, referred as a “mobile station”) and base station apparatus(hereafter, referred to as a “base station”). Further, it is consideredthat several-bit information is transmitted to request scheduling forallocating radio resource, and the like to decrease the connection timebetween the mobile station and base station. Meanwhile, the intendedpurpose of the synchronized random access channel is to make ascheduling request (Non-patent Document 2).

On the non-synchronized random access channel, only a preamble istransmitted to acquire synchronization. This preamble contains asignature that is a signal pattern indicative of information, and bypreparing a few tens of kinds of signatures, it is possible to designateseveral-bit information. Currently, it is anticipated that informationof 4˜6 bits is transmitted, and that 16˜64 kinds of signatures areprepared. For example, expected as the information of 4˜6 bits are areason of random access, downlink path-loss/CQI (Channel QualityIndicator), random ID and the like. Particularly, in the reason ofrandom access, it is studied to designate handover, initial access,maintenance of synchronization, scheduling request or the like to makethe access procedure efficient.

Herein, a configuration example of signatures included in the preambleis described with reference to FIGS. 16 and 17. FIG. 16 shows aconfiguration example of signatures in the case of splitting each kindof information to a field to designate the information. Shown herein isthe case of allocating 2 bits to the reason of random access, 1 bit torandom ID, and 1 bit to CQI. In the reason of random access, forexample, “00” is selected in designating handover, while “11” isselected in designating maintenance of synchronization. Meanwhile, FIG.17 shows the case of flexibly selecting the reason of random access, CQIand random ID to designate the information. The case is shown that codesfrom 0 to 15 are assigned to combinations of the reason of randomaccess, CQI and random ID.

FIG. 18 is a sequence chart to explain an example of a conventionalprocedure of random access. FIG. 18 shows the procedure of random accessin the case of using a non-synchronized random access channel. As shownin FIG. 18, in the conventional procedure of random access, a mobilestation first selects a signature based on the reason of random access,downlink path-loss/CQI information, random ID and the like (step(hereinafter, abbreviated as “ST”) 1801). Then, the mobile stationtransmits a preamble (random access preamble) containing the selectedsignature on the non-synchronized random access channel (ST1802).

Upon receiving the preamble from the mobile station, the base stationcalculates a synchronization timing deviation between the mobile stationand base station from the preamble, and performs scheduling fortransmitting an L2/L3 (Layer2/Layer3) message (ST1803). Then, the basestation assigns C-RNTI (Cell-Radio Network Temporary Identity) to themobile station requiring C-RNTI from the random access reason, andtransmits synchronization timing deviation information (synchronizationinformation), scheduling information, signature ID number and C-RNTI(ST1804).

Upon receiving the information from the base station, the mobile stationextracts a response from the base station including the transmittedsignature ID number (ST1805). Then, the mobile station transmits anL2/L3 message with radio resources subjected to scheduling in the basestation (ST1806). Upon receiving the L2/L3 message from the mobilestation, the base station sends back a response corresponding to themessage (ST1807).

A problem of such random access is that a collision occurs in the casethat a plurality of different mobile stations selects the same signatureand random access channel. When a plurality of mobile stations selectsthe same signature and transmits the signature with a radio resourceblock having the same time and frequency i.e. on the same random accesschannel, a collision occurs in the preamble (ST1802) as shown in FIG.18.

When the base station cannot detect the preamble (ST1802) due to such acollision, the base station cannot send back the response (ST1804)including the synchronization information and the like. In this case,the mobile station cannot receive the response (ST1804) from the basestation, and therefore, needs to select a signature and random accesschannel again after a lapse of predetermined time to perform randomaccess.

Meanwhile, when the base station can detect the preamble (ST1802), thebase station calculates L2/L3 message scheduling and synchronizationtiming deviation, and sends back a response (ST1804) to the mobilestation. However, a plurality of mobile stations receives the response(ST1804) from the base station. Therefore, the plurality of mobilestations transmits the L2/L3 message (ST1806) with radio resourcessubjected to scheduling, and as a result, the collision occurs in theL2/L3 message (ST1806).

When the base station cannot detect the L2/L3 message (ST1806) due tosuch a collision, the base station cannot send back the response(ST1807). In this case, the mobile station cannot receive the response(ST1807) from the base station, and therefore, needs to select asignature and random access channel again after a lapse of predeterminedtime to perform random access. Thus, when a plurality of mobile stationsselects the same signature and random access channel, the collision canoccur, while when the collision occurs, the time up to ST1807 as shownin FIG. 18 is required at the maximum until the collision is detected.

Meanwhile, when a mobile station capable of executing random access islocated in a position as shown in FIG. 19, handover is executed. Alsowhen handover is executed, the above-mentioned random access isperformed.

Described herein is an example of a procedure of random access at thetime of executing handover. FIG. 20 is a sequence chart to explain anexample of a procedure of random access at the time of executinghandover. In addition, as in FIG. 18, FIG. 20 shows the procedure ofrandom access in the case of using a non-synchronized random accesschannel.

As shown in FIG. 20, in the procedure of random access at the time ofexecuting handover, as a preparatory stage, a mobile station firstmeasures radio conditions of adjacent base stations (ST2001). Then, themobile station transmits the measurement result (measurement report) tobase station A that is a base station (hereinafter, “local-base station”as appropriate) currently holding the mobile station (ST2002). Uponreceiving the measurement result from the mobile station, the basestation A selects an optimal base station from the measurement result(ST2003). In addition, herein, base station B is assumed to be selectedas an optimal base station. Then, the base station A transmits ahandover request command to the base station B that is a handoverdestination (ST2004).

Upon receiving the handover request command from the base station A, thebase station B assigns C-RNTI to the mobile station performing handover(ST2005). Then, as a response to the handover request, the base stationB notifies the base station A of a handover request acknowledge commandincluding the C-RNTI (ST2006). Upon receiving the handover requestacknowledge command from the base station B, the base station Atransmits a handover command including the C-RNTI to the mobile station(ST2007).

Upon receiving the handover command from the base station A, the mobilestation acquires synchronization on downlink of the base station B, andconfirms a position of the random access channel from the broadcastchannel (ST2008). When the downlink synchronization is acquired, themobile station selects one signature from among signatures such that thereason of random access is handover (ST2009). Then, the mobile stationtransmits a preamble (random access preamble) containing the selectedsignature to the base station B on the random access channel (ST2010).

Upon detecting the signature from the preamble received from the mobilestation, the base station B calculates a synchronization timingdeviation, and performs scheduling of uplink for the mobile station totransmit a handover completion message (ST2011). Then, the base stationB transmits synchronization timing deviation information(synchronization information), scheduling information and signature IDnumber (ST2012). In addition, in the case that the random access reasonis handover, C-RNTI is be forehand notified, and therefore, is nottransmitted.

Upon receiving the information to the mobile station from the basestation B, the mobile station corrects the synchronization timingdeviation based on the synchronization timing deviation information(synchronization information) (ST2013). Then, the mobile stationtransmits a handover completion message with radio resources subjectedto scheduling (ST2014). Upon receiving the handover completion messagefrom the mobile station, the base station sends back a responsecorresponding to the message (ST2015).

Non-patent Document 1: R1-050850 “Physical Channel and Multiplexing inEvolved UTRA Uplink”, 3GPP TSG RAN WG1 Meeting #42 London, UK, Aug.29-Sep. 2, 2005

Non-patent Document 2: 3GPP TR (Technical Report) 25.814, V7.0.0(2006-06), Physical layer aspects for evolved Universal TerrestrialRadio Access (UTRA)

DISCLOSURE OF INVENTION Problems to be Solved by the Invention

In random access such that the reason is handover, since communicationsare disconnected when a collision with another mobile station occurs, itis desired that a collision does not occur. However, in the mobilecommunication system such that the mobile station randomly selects asignature and random access channel, the fact is that it is not possibleto completely eliminate the collision probability. In addition, when anuplink scheduling channel is used in order for the collision not tooccur, since uplink synchronization is not achieved between the mobilestation and base station, the base station cannot receive data from themobile station.

Further, there is a case that a base station other than the base stationas a handover destination responds to random access from the mobilestation (herein, for example, in the case that the base station-A andbase station-C as shown in FIG. 19 respond), and a problem arises thatexcess downlink radio resources are allocated.

Furthermore, it is expected that when a mobile station receives a pagingmessage notified from the base station to page the mobile station, themobile station performs random access as a response to paging. At thetime of executing such random access as a response to paging, when acollision occurs, another problem occurs that communication efficiencydegrades, as well as the connection time being long.

The present invention was carried out in view of such problems, and itis an object to provide a mobile communication system, base stationapparatus and mobile station apparatus capable of preventing a collisionfrom occurring at the time of random access in cases such as handover,response to paging and the like where the mobile station apparatusperforms random access in response to directions from the base stationapparatus.

Means for Solving the Problem

(1) To attain the above-mentioned object, the present invention tookmeasures as described below. In other words, a mobile communicationsystem according to the invention is a mobile communication system inwhich a mobile station apparatus uses a signature of a beforehanddetermined signature group at the time of random access with a basestation apparatus, and is characterized in that the signature group iscomprised of a signature group managed by the base station apparatus andanother signature group managed by the mobile station apparatus.

Thus, since the signature group used by the mobile station apparatus atthe time of random access is provided with the signature group managedby the base station apparatus, random access can be carried out underthe initiative of the base station apparatus, and it is thereby possibleto prevent a collision from occurring at the time of random access incases such as handover, response to paging and the like where the mobilestation apparatus performs random access in response to directions fromthe base station apparatus.

(2) The mobile communication system according to the invention ischaracterized in that the signature group managed by the base stationapparatus includes signatures associated with particular random accessreasons to be selected by the base station apparatus.

Thus, signatures associated with particular random access reasons areselected by the base station apparatus, it is thereby possible to assigndifferent signatures for each mobile station apparatus, and it ispossible to prevent the occurrence of collision caused by mobilestations selecting the same signature at the time of random access.

(3) The mobile communication system of the invention is characterized inthat the signature group managed by the base station apparatus includessignatures that are preferentially selected by an adjacent base stationapparatus.

Thus, since the signature group managed by the base station apparatusincludes signatures that are preferentially selected by an adjacent basestation, signatures to select can be adjusted with the adjacent basestation apparatus, and it is thereby possible to reduce collisions thatcould occur with the adjacent base station at the time of random access.

(4) The mobile communication system of the invention is characterized inthat the base station apparatus shares information of respectivelyselected signatures with the adjacent base station.

Thus, since the information of respectively selected signatures isshared with the adjacent base station, signatures to select can beadjusted with the adjacent base station, and it is thereby possible toreduce collisions that could occur with the adjacent base station at thetime of random access.

(5) For example, the mobile communication system of the invention ischaracterized in that the signature group managed by the base stationapparatus includes signatures associated with handover as the particularrandom access reason.

Thus, since the signature group managed by the base station apparatusincludes signatures associated with handover as the particular randomaccess reason, it is possible to prevent communications from beingdisconnected due to the collision in random access performed at the timeof handover.

(6) Particularly, the mobile communication system of the invention ischaracterized in that a signature selected by the base station apparatusis included in a handover message for starting execution of handover andtransmitted to the mobile station apparatus.

Thus, a signature selected by the base station apparatus is included ina handover message and transmitted to the mobile station apparatus, andit is thereby possible to transmit a signature selected by the basestation apparatus to the mobile station apparatus exploiting analready-existing signal.

(7) Further, the mobile communication system of the invention ischaracterized in that the signature group managed by the base stationapparatus includes signatures associated with a response at the time ofreceiving paging as the particular random access reason.

Thus, since the signature group managed by the base station apparatusincludes signatures associated with a response at the time of receivingpaging as the particular random access reason, it is possible to preventthe connection time from being long due to the collision in randomaccess at the time of responding to paging.

(8) Further, the mobile communication system of the invention ischaracterized in that a signature selected by the base station isincluded in a paging message for paging the mobile station apparatus andtransmitted to the mobile station apparatus.

Thus, a signature selected by the base station apparatus is included ina paging message and transmitted to the mobile station apparatus, and itis thereby possible to transmit a signature selected by the base stationapparatus to the mobile station apparatus exploiting an already-existingsignal.

(9) The mobile communication system of the invention is characterized byvarying a ratio between the signature group managed by the base stationapparatus and the signature group managed by the mobile stationapparatus corresponding to communication conditions of the base stationapparatus and the mobile station apparatus communicating with the basestation apparatus.

Thus, since the ratio is varied between the signature group managed bythe base station apparatus and the signature group managed by the mobilestation apparatus corresponding to current communication conditions, itis possible to determine an optimal ratio between both signature groupscorresponding to current communication conditions, and it is possible toefficiently prevent a collision from occurring at the time of randomaccess.

(10) Further, the mobile communication system of the invention ischaracterized by including details on the signature group managed by thebase station apparatus and the signature group managed by the mobilestation apparatus in broadcast information to transmit to the mobilestation apparatus.

Thus, details on the signature group managed by the base stationapparatus and the signature group managed by the mobile stationapparatus are included in the broadcast information and transmitted tothe mobile station apparatus, and it is thereby possible to transmitdetails on the signature groups managed by the base station apparatusand the mobile station apparatus to the mobile station apparatusexploiting an already-existing signal.

(11) Furthermore, the mobile communication system of the invention ischaracterized in that the base station apparatus further selects afrequency band position and/or time position of random access, whileselecting the signature.

Thus, as well as the signature, the base station apparatus selects afrequency band position and/or time position of random access, and it isthereby possible to decrease the probability of collision at the time ofrandom access, by selecting the frequency band position and/or timeposition of the random access channel.

(12) A base station apparatus of the invention is a base stationapparatus connecting to a mobile station apparatus using a signature ofa beforehand determined signature group at the time of random access,and is characterized by having a signature selecting section thatselects a signature associated with a particular random access reasonfrom the signature group, and a signature managing section that managesthe signature selected by the signature selecting section.

Thus, since the signature selecting section selects a signatureassociated with a particular random access reason from the signaturegroup used at the time of random access, it is possible to assigndifferent signatures for each mobile station apparatus, and it ispossible to prevent the occurrence of collision caused by mobilestations selecting the same signature at the time of random access.

(13) The base station apparatus of the invention is characterized inthat the signature associated with a particular random access reasonincludes a signature to be preferentially selected by an adjacent basestation apparatus, and that the signature selecting sectionpreferentially selects a signature except the signature to bepreferentially selected by the adjacent base station apparatus.

Thus, since the signature selecting section preferentially selects asignature except the signature to be preferentially selected by theadjacent base station apparatus, signatures to select can be adjustedwith the adjacent base station apparatus, and it is thereby possible toreduce collisions that could occur with the adjacent base station at thetime of random access.

(14) Further, the base station apparatus of the invention ischaracterized in that the signature associated with a particular randomaccess reason includes a signature to be preferentially selected by anadjacent base station apparatus, and that the signature managing sectionshares information of respectively selected signatures with the adjacentbase station apparatus.

Thus, since the signature managing section shares the information ofrespectively selected signatures with the adjacent base stationapparatus, signatures to select can be adjusted with the adjacent basestation, and it is thereby possible to reduce collisions that couldoccur with the adjacent base station at the time of random access.

(15) For example, the base station apparatus of the invention ischaracterized in that the signature selecting section selects asignature associated with handover as the particular random accessreason.

Thus, since the signature selecting section selects a signatureassociated with handover, it is possible to prevent communications frombeing disconnected due to the collision in random access performed atthe time of handover.

(16) Particularly, the base station apparatus of the invention ischaracterized in that a signature selected by the signature selectingsection is included in a handover message for starting execution ofhandover and transmitted to the mobile station apparatus.

Thus, the selected signature is included in a handover message andtransmitted to the mobile station apparatus, and it is thereby possibleto transmit a signature selected by the base station apparatus to themobile station apparatus exploiting an already-existing signal.

(17) Further, the base station apparatus of the invention ischaracterized in that the signature selecting section selects asignature associated with a response at the time of receiving paging asthe particular random access reason.

Thus, since the signature selecting section selects a signatureassociated with a response in receiving paging, it is possible toprevent the connection time from being long due to the collision inrandom access at the time of responding to paging.

(18) Particularly, the base station apparatus of the invention ischaracterized in that a signature selected by the signature selectingsection is included in a paging message for paging the mobile stationapparatus and transmitted to the mobile station apparatus.

Thus, the selected signature is included in a paging message andtransmitted to the mobile station apparatus, and it is thereby possibleto transmit a signature selected by the base station apparatus to themobile station apparatus exploiting an already-existing signal.

(19) The base station apparatus of the invention is characterized byincreasing or decreasing signatures capable of being selected by thesignature selecting section corresponding to communication conditionswith the mobile station apparatus communicating with the base stationapparatus.

Thus, since signatures capable of being selected by the signatureselecting section are increased or decreased corresponding tocommunication conditions with the mobile station apparatus communicatingwith the base station apparatus, it is possible to select the optimalnumber of signatures corresponding to current communication conditions,and it is possible to efficiently prevent a collision from occurring atthe time of random access.

(20) Further, the base station apparatus of the invention ischaracterized by including in broadcast information a result ofincreasing or decreasing signatures capable of being selected by thesignature selecting section corresponding to communication conditionswith the mobile station apparatus communicating with the base stationapparatus to transmit to the mobile station apparatus.

Thus, a result of increasing or decreasing signatures capable of beingselected by the signature selecting section is included in the broadcastinformation and transmitted to the mobile station apparatus, and it isthereby possible to transmit the result of increasing or decreasingsignatures capable of being selected by the signature selecting sectionexploiting an already-existing signal.

(21) The base station apparatus of the invention is characterized inthat the signature selecting section selects the signature associatedwith a particular random access reason, and a frequency band positionand/or time position of random access, and that the signature managingsection manages the signature selected by the signature selectingsection, and the frequency band position and/or time position of randomaccess.

Thus, as well as the signature associated with a particular randomaccess reason, the frequency band position and/or time position ofrandom access is selected by the signature selecting section and managedby the signature managing section, and it is thereby possible todecrease the probability of collision at the time of random access, byselecting the frequency band position and/or time position of the randomaccess channel.

(22) A mobile station apparatus of the invention is a mobile stationapparatus connecting to a base station apparatus to transmit a signatureof a beforehand determined signature group at the time of random access,and is characterized by having a receiving section that receives asignal transmitted from the base station apparatus, a control dataextracting section that extracts a signature from the signal, and atransmitting section that transmits a preamble corresponding to theextracted signature to the base station apparatus or another basestation apparatus.

Thus, since the mobile station apparatus receives a signal transmittedfrom the base station apparatus, extracts a signature from the signal,and transmits a preamble corresponding to the extracted signature to thebase station apparatus or another base station apparatus, random accesscan be carried out under the initiative of the base station apparatus.It is thereby possible to prevent a collision from occurring at the timeof random access in cases such as handover, response to paging and thelike where the mobile station apparatus performs random access inresponse to directions from the base station apparatus. Further, thebase station apparatus refers to the preamble received from the mobilestation apparatus, and when the signature is not assigned by the basestation apparatus, does not respond to the mobile station apparatus ondownlink to leave, and it is thereby possible to eliminate wasteful useof radio resources on downlink.

ADVANTAGEOUS EFFECT OF THE INVENTION

According to the invention, since the signature group used by the mobilestation apparatus at the time of random access is provided with thesignature group managed by the base station apparatus, random access canbe carried out under the initiative of the base station apparatus, andit is thereby possible to prevent a collision from occurring at the timeof random access in cases such as handover, response to paging and thelike where the mobile station apparatus performs random access inresponse to directions from the base station apparatus.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a diagram to explain a setting example of signatures in acommunication system according to Embodiment 1 of the invention;

FIG. 2 is a block diagram showing an example of a configuration of abase station included in the communication system according toEmbodiment 1;

FIG. 3 is a block diagram showing an example of a configuration of amobile station included in the communication system according toEmbodiment 1;

FIG. 4 is a sequence chart to explain an example of a random accessprocedure at the time of executing handover in the communication systemaccording to Embodiment 1;

FIG. 5 is a diagram to explain a setting example of signatures in acommunication system according to Embodiment 2 of the invention;

FIG. 6 is a sequence chart to explain an example of a random accessprocedure at the time of executing handover in a communication systemaccording to Embodiment 3 of the invention;

FIG. 7 is a diagram to explain a setting example of signatures in acommunication system according to Embodiment 4 of the invention;

FIG. 8 is a sequence chart to explain an example of a random accessprocedure at the time of receiving paging in the communication systemaccording to Embodiment 4.

FIG. 9 is a diagram to explain the summary of setting of signatures in acommunication system according Embodiment 5 of the invention;

FIG. 10 is a diagram showing a table for determining the numbers ofbase-station managed signatures and mobile-station managed signatures inthe communication system according to Embodiment 5;

FIG. 11 is a diagram to explain a setting example of signatures in thecommunication system according to Embodiment 5;

FIG. 12 is a block diagram showing an example of a configuration of abase station included in the communication system according toEmbodiment 5;

FIG. 13 is a block diagram showing an example of a configuration of amobile station included in the communication system according toEmbodiment 5;

FIG. 14 is a diagram to explain a configuration of uplink in EUTRA;

FIG. 15 is a diagram to explain an uplink random access channel inE-UTRA;

FIG. 16 is a diagram to explain a conventional configuration example ofsignatures;

FIG. 17 is a diagram to explain another conventional configurationexample of signatures;

FIG. 18 is a sequence chart to explain an example of a conventionalprocedure of random access;

FIG. 19 is a diagram to explain locations of base stations wherehandover arises; and

FIG. 20 is a sequence chart to explain another example of a conventionalprocedure of random access at the time of executing handover.

DESCRIPTION OF SYMBOLS

-   100 Base station apparatus (Base station)-   101 Data control section-   102 OFDM modulation section-   103 Scheduling section-   104 Radio section-   105 Channel estimation section-   106 DFT-S-OFDM demodulation section-   107 Control data extracting section-   108 Preamble detecting section-   109 Signature selecting section-   110 Signature managing section-   200 Mobile station apparatus (Mobile station)-   201 Data control section-   202 DFT-S-OFDM modulation section-   203 Scheduling section-   204 Signature selecting section-   205 Preamble generating section-   206 Synchronization correcting section-   207 Radio section-   208 Channel estimation section-   209 OFDM demodulation section-   210 Control data extracting section

BEST MODE FOR CARRYING OUT THE INVENTION

Embodiments of the invention will be described below with reference toaccompanying drawings. A mobile communication system (hereinafter,referred to as a “communication system” as appropriate) according to theEmbodiments of the invention enables part of management (selection) ofsignatures that has conventionally been performed in a mobile stationapparatus (hereinafter, referred to as a “mobile station”) irrespectiveof an intended purpose of random access to be performed in a basestation apparatus (hereinafter, referred to as a “base station”)corresponding to a reason of random access.

In other words, in the communication system according to theEmbodiments, corresponding to the intended purpose of random access, themobile station separates signatures (hereinafter, referred to as“base-station managed signatures” as appropriate) managed by the basestation apparatus and signatures (hereinafter, referred to as“mobile-station managed signatures” as appropriate) managed by themobile station to use. In other words, the base-station managedsignatures are signatures selectable in the base station, and themobile-station managed signatures are signatures selectable in themobile station.

Embodiment 1

FIG. 1 is a diagram to explain a setting example of signatures in acommunication system according to Embodiment 1 of the invention. In thecommunication system according to Embodiment 1, as shown in FIG. 1,signature ID numbers (hereinafter, referred to as “signature numbers”) 1to 24 are allocated as base-station managed signatures, and signaturenumbers 25 to 64 are allocated as mobile-station managed signatures.Particularly, in the communication system according to Embodiment 1,signature numbers 1 to 14 are set for handover as their intendedpurpose, and signature numbers 25 to 64 are set for scheduling request,initial access, and synchronization maintenance (synchronization) astheir intended purpose.

Described herein are configurations of the base station and mobilestation included in the communication system according to Embodiment 1where signatures are thus set. FIG. 2 is a block diagram showing anexample of the configuration of the base station included in thecommunication system according to Embodiment 1. FIG. 3 is a blockdiagram showing an example of the configuration of the mobile stationincluded in the communication system according to Embodiment 1.

As shown in FIG. 2, the base station 100 is comprised of a data controlsection 101, OFDM modulation section 102, scheduling section 103, radiosection 104, channel estimation section 105, DFT-Spread-OFDMdemodulation section (DFT-S-OFDM demodulation section) 106, control dataextracting section 107, preamble detecting section 108, signatureselecting section 109 and signature managing section 110.

The data control section 101 receives inputs of control data and userdata, and corresponding to directions from the scheduling section 103,performs mapping of the control data on a downlink shared controlchannel, downlink synchronized channel, downlink pilot channel anddownlink shared control signaling channel, while further performingmapping of transmission data (user data) to each mobile station on ashared data channel. The OFDM modulation section 102 performs datamodulation, serial/parallel transform of an input signal, IFFT (InverseFast Fourier Transform), CP (Cyclic Prefix) insertion, filtering and thelike, and thus performs OFDM signal processing to generate an OFDMsignal.

The scheduling section 103 is comprised of a DL scheduling section 103 athat performs downlink scheduling, and UL scheduling 103 b that performsuplink scheduling. The DL scheduling section 103 a performs schedulingto perform mapping of user data on each downlink channel from CQIinformation notified from the mobile station, and data information ofeach user notified from a higher layer. The UL scheduling section 103 bperforms scheduling to perform mapping of user data on each uplinkchannel from an uplink radio propagation path estimation result from thechannel estimation section 105, and resource allocation request from themobile station.

The radio section 104 up-converts the OFDM modulated data into aradio-frequency signal to transmit to the mobile station. Further, theradio section 104 receives uplink data from the mobile station,down-converts the data to a baseband signal, and outputs the receptiondata to the channel estimation section 105, DFT-S-OFDM demodulationsection 106 and preamble detecting section 108.

The channel estimation section 105 estimates radio propagation pathcharacteristics from the uplink pilot channel UPiCH, and outputs anestimation result to the DFT-S-OFDM demodulation section 106. Further,to perform uplink scheduling, the section 105 outputs the radiopropagation path estimation result to the scheduling section 103. Inaddition, as an uplink communication system, a single-carrier system isassumed such as DFT-S-OFDM and the like, but a multicarrier system isalso allowed such as the OFDM system and the like.

The DFT-S-OFDM demodulation section 106 demodulates the reception dataoutput from the radio section 104, corresponding to the radiopropagation path estimation result from the channel estimation result105. The control data extracting section 107 divides the reception datainto user data (uplink shared data channel USDCH) and control data(uplink shared control signaling channel USCSCH). Among the dividedcontrol data, the downlink CQI information is output to the schedulingsection 103, and the other control data and user data is output to thehigher layer.

The preamble detecting section 108 detects a preamble, calculates asynchronization timing deviation amount, and reports the signaturenumber and synchronization timing deviation amount. When the signaturenumber is a base-station managed signature number described later, thesection 108 checks whether or not the signature is used by the basestation 100 with the signature managing section 110. As a result of thecheck, when the signature is used by the base station 100, the section108 reports the signature number and synchronization timing deviationamount to the higher layer. On the other hand, when the signature is notused by the base station 100, the section 108 does not report thesignature number and synchronization timing deviation amount to thehigher layer.

The signature selecting section 109 selects a signature corresponding todirections from the higher layer to notify the higher layer andsignature managing section 110. In selecting a signature, the section109 checks with the signature managing section 110 for signature numbersbeing used, and selects one from among signatures except the signaturebeing used.

The signature managing section 110 stores a signature ID number selectedin the signature selecting section 109, and deletes the base-stationmanaged signature detected in the preamble detecting section 108 fromstored signatures.

Meanwhile, as shown in FIG. 3, the mobile station 200 is comprised of adata control section 201, DFT-S-OFDM modulation section 202, schedulingsection 203, signature selecting section 204, preamble generatingsection 205, synchronization correcting section 206, radio section 207,channel estimation section 208, OFDM demodulation section 209 andcontrol data extracting section 210.

The data control section 201 receives inputs of user data and controldata, and corresponding to directions from the scheduling section 203,performs mapping of the data on an uplink scheduling channel. TheDFT-S-OFDM modulation section 202 modulates the data, performsDFT-S-OFDM signal processing such as DFT transform, subcarrier mapping,IFFT, CP (Cyclic Prefix) insertion, filtering and the like, andgenerates a DFT-Spread-OFDM signal. In addition, as an uplinkcommunication system, a single-carrier system is assumed such asDFT-Spread OFDM and the like, but a multicarrier system is also allowedsuch as the OFDM system.

The scheduling section 203 performs scheduling to perform mapping ofuser data on each uplink channel from CQI information notified from thechannel estimation section 208 described later, and schedulinginformation notified from the higher layer.

The signature selecting section 204 selects a signature number to use inrandom access corresponding to directions from the higher layer. Asdirections from the higher layer, the purpose of random access isnotified. When the notified purpose is a base-station managed purposesuch as handover, paging or the like, the section 204 selects thesignature number instructed from the higher layer. Meanwhile, when thepurpose is a mobile-station managed purpose, the section 204 randomlyselects one from among mobile-station managed signatures sortedaccording to the purposes, corresponding to the purpose, and outputs theselected signature number to the preamble generating section 205.

The preamble generating section 205 generates a preamble with thesignature number selected in the signature selecting section 204 tooutput to the DFT-S-OFDM modulation section 202. The synchronizationcorrecting section 206 determines transmission timing from thesynchronization information output from the control data extractingsection 210 described later, and outputs data modulated to adapt to thetransmission timing to the radio section 207. The radio section 207 setsa radio frequency, and up-converts the modulated data into aradio-frequency signal to transmit to the base station 100. Further, theradio section 207 receives downlink data from the base station 100 todown-convert into a baseband signal, and outputs reception data to theOFDM demodulation section 209.

The channel estimation section 208 estimates radio propagation pathcharacteristics from the downlink pilot channel, and outputs theestimation result to the OFDM demodulation section 209. Further, thesection 208 converts the result into CQI information to notify the basestation 100 of the radio propagation path estimation result, and outputsthe CQI information to the scheduling section 203.

The OFDM demodulation section 209 demodulates the reception data outputfrom the radio section 207, corresponding to the radio propagation pathestimation result of the channel estimation section 208.

The control data extracting section 210 divides the reception data intouser data and control data. The scheduling information in the dividedcontrol data is output to the scheduling section 203, uplinksynchronization information is output to the synchronization correctingsection 206, and the other control data and user data is output to thehigher layer.

Described next is an example of a random access procedure at the time ofexecuting handover in the communication system having theabove-mentioned configuration. FIG. 4 is a sequence chart to explain anexample of a random access procedure at the time of executing handoverin the communication system according to Embodiment 1. In addition, itis assumed herein that the mobile station 200 is currently held by abase station 100A (hereinafter, referred to as a “base station A” asappropriate).

As shown in FIG. 4, in the random access procedure at the time ofexecuting handover in the communication system according to Embodiment1, as a preparatory stage, the mobile station 200 first measures radioconditions of adjacent base stations (ST401). Then, the mobile station200 transmits the measurement result (measurement report) to the basestation A that is the local-base station (ST402). Upon receiving themeasurement result from the mobile station, the base station A selectsan optimal base station from the measurement result (ST403). Inaddition, herein, as the optimal base station, a base station 100B(hereinafter, referred to as a “base station B” as appropriate) isassumed to be selected. Then, the base station A transmits a handoverrequest command to the base station B that is a handover destination(ST404).

Upon receiving the handover request command from the base station A, thebase station B selects one signature from among base-station managedsignatures (ST405). Herein, a signature of signature number 1 is assumedto be selected. In this case, to avoid a collision of random access, thebase station B selects a signature from among the base-station managedsignatures except signatures being used in the base station B. Then,after assigning C-RNTI to the mobile station 200 for performinghandover, the base station B notifies the base station A of a handoverrequest acknowledge command including the signature number and C-RNTI asa response to the handover request command (ST406).

Upon receiving the handover request acknowledge command from the basestation B, the base station A transmits a handover command (handovermessage) including the signature number and C-RNTI to the mobile station200 (ST407). Upon receiving the handover command from the base stationA, the mobile station 200 acquires downlink synchronization with thebase station B, and checks a position of the random access channel fromthe broadcast channel (ST408). After acquiring downlink synchronization,the mobile station 200 transmits a preamble (random access preamble)including a signature of the signature number added to the handovercommand i.e. the signature of signature number 1 to the base station Bon the random access channel (ST409).

Upon detecting the signature from the preamble received from the mobilestation 200, the base station B determines whether the signature isassigned by the base station B (ST410). Herein, since the base station Breceives the signature of signature number 1 and this signature ofsignature number 1 is assigned by the base station B, the base station Bcalculates a synchronization timing deviation amount and performsscheduling for transmitting a handover completion message (ST411). Then,the base station B transmits the synchronization timing deviationinformation (synchronization information), scheduling information andC-RNTI (ST412). In this case, since C-RNTI is beforehand notified, thesignature number is not required as identification information forchecking data to the mobile station 200 by the station 200, and C-RNTIis enough.

In addition, in the determination in ST410, when the base station Bdetermines that the signature received from the mobile station 200 isnot the signature assigned by the base station B, the base station Bdoes not respond to the mobile station 100 to leave (ST413).

Upon receiving the information to the mobile station 200 from the basestation B, the station 200 corrects the synchronization timing deviationbased on the synchronization timing deviation information(synchronization information) (ST414). Then, the mobile station 200transmits a handover completion message with radio resources subjectedto scheduling (ST415). Upon receiving the handover completion messagefrom the mobile station 200, the base station B sends back a response tothe mobile station 200 in response to the message (ST416).

Thus, in the communication system according to Embodiment 1, since thesignature group used by the mobile station 200 at the time of randomaccess is provided with the signature group (base-station managedsignature group) managed by the base station 100, random access can becarried out under the initiative of the base station 100, and it isthereby possible to prevent a collision from occurring at the time ofrandom access in the case that the mobile station 200 performs randomaccess in response to directions from the base station 100.

Further, in the communication system according to Embodiment 1, thebase-station managed signatures include signatures which are associatedwith particular random access reasons such as handover and the like andselected by the base station 100. The base station 100 selects thesignatures thus associated with particular random access reasons, and isthereby capable of assigning different signatures for each mobilestation 200, and it is possible to prevent the occurrence of collisioncaused by the mobile stations 200 selecting the same signature at thetime of random access.

Particularly, in the communication system according to Embodiment 1,since the base-station managed signatures include signatures associatedwith handover as the random access reason, it is possible to prevent acollision from occurring in random access performed at the time ofhandover. As a result, it is possible to prevent communications frombeing disconnected due to the collision. Further, when the base stationA that is the local-base station and adjacent base station (not shown)receive a signature for handover from the mobile station 200, in thecase that the signature is not assigned by the station A or station B,the station A or B does not send back a response to the mobile station200 on downlink, and downlink radio resources are not used uselessly.

In addition, in the communication system according to Embodiment 1, asignature selected by the base station 100 is included in a handovermessage and transmitted to the mobile station 200, and therefore, it ispossible to transmit the signature selected by the base station 100 tothe mobile station 200 exploiting an already-existing signal.

Embodiment 2

In the mobile communication system according to Embodiment 1, the basestation 100 selects a signature, while managing the information ofsignatures used in the base station 100, thereby preventing thecollision in the base station 100 in random access at the time ofhandover. However, when mobile stations 200 held in the adjacent basestation concurrently perform handover and select the same signature, thecollision can occur. In a communication system according to Embodiment2, signature numbers to select are adjusted between adjacent basestations, and it is intended to reduce collisions that could occur inrandom access at the time of handover.

In addition, configurations of the base station 100 and mobile station200 constituting the communication system according to Embodiment 2 arethe same as those in Embodiment 1, and descriptions thereof are omitted.Further, signatures in the communication system according to Embodiment2 differ from those in the communication system according to Embodiment1 in the respect that a range of signatures for each base station topreferentially use is provided in base-station managed signatures.

FIG. 5 is a diagram to explain a setting example of signatures in thecommunication system according to Embodiment 2 of the invention. In thecommunication system according to Embodiment 2, as shown in FIG. 5,signature numbers 1 to 24 allocated as base-station managed signaturesare provided with ranges respectively for base stations (herein, basestation A to base station C) to preferentially use. More specifically,the range (hereinafter, referred to as a “base-station A preferentiallyused range” as appropriate) for the base station A to preferentially useis signature numbers 1 to 8, the range (hereinafter, referred to as a“base-station B preferentially used range” as appropriate) for the basestation B to preferentially use is signature numbers 9 to 16, and therange (hereinafter, referred to as a “base-station C preferentially usedrange” as appropriate) for the base station C to preferentially use issignature numbers 17 to 24.

In this case, the base station A allocates signatures to mobile stationsperforming handover in ascending order of the signature number startingwith signature number 1. Similarly, the base station B allocatessignatures to mobile stations performing handover in ascending order ofthe signature number starting with signature number 9, and the basestation C allocates signatures to mobile stations performing handover inascending order of the signature number starting with signature number17. Then, in each base station, when all the signatures in the range topreferentially use are allocated to mobile stations, the base stationselects a signature of the number with a low priority in the range foranother station to preferentially use. For example, when the basestation A allocates all the signatures of signature numbers 1 to 8 tomobile stations, the base station A selects a signature in ascendingorder starting with the signature numbered 16 given the lowest priorityin the base-station B preferentially used range, or the signaturenumbered given the lowest priority in the base-station C preferentiallyused range.

Thus, in the communication system according to Embodiment 2, ranges ofsignature numbers to preferentially use are beforehand determined amongadjacent base stations, selection of signatures is thus adjusted, and itis thereby possible to reduce collisions that could occur with theadjacent base station in random access at the time of handover.

Embodiment 3

In the communication system according to Embodiment 2, to reducecollisions that could occur with the adjacent base station in randomaccess at the time of handover, ranges of signature numbers topreferentially use are beforehand determined among adjacent basestations, and selection of signatures is adjusted. In contrast thereto,in a communication system according to Embodiment 3, signatureinformation is shared among adjacent base stations, and it is intendedto reduce collisions that could occur with the adjacent base station inrandom access at the time of handover.

In addition, configurations of the base station 100 and mobile station200 constituting the communication system according to Embodiment 3 arethe same as those in Embodiment 1, and descriptions thereof are omitted.Further, with respect to signatures in the communication systemaccording to Embodiment 3, as in the communication system according toEmbodiment 1, signature numbers 1 to 24 are allocated as base-stationmanaged signatures, and signature numbers 25 to 64 are allocated asmobile-station managed signatures.

Described below is an example of a random access procedure at the timeof executing handover in the communication system according toEmbodiment 3. FIG. 6 is a sequence chart to explain an example of arandom access procedure at the time of executing handover in thecommunication system according to Embodiment 3. In addition, it isassumed herein that the mobile station 200 is currently held by the basestation A, and that the base station A is adjacent to the base station Band base station 100 c (hereinafter, referred to as a “base station C”as appropriate) (for example, see FIG. 19).

As shown in FIG. 6, in the random access procedure at the time ofexecuting handover in the communication system according to Embodiment3, as a preparatory stage, the mobile station 200 first measures radioconditions of adjacent base stations (ST601). Then, the mobile station200 transmits the measurement result (measurement report) to the basestation A that is the local-base station (ST602). Upon receiving themeasurement result from the mobile station, the base station A selectsan optimal base station from the measurement result (ST603). Inaddition, herein, as the optimal base station, the base station B isassumed to be selected. Then, the base station A transmits a handoverrequest command to the base station B that is a handover destination(ST604).

Upon receiving the handover request command from the base station A, thebase station B selects one signature from among base-station managedsignatures (ST605). Herein, a signature of signature number 1 is assumedto be selected. In this case, to avoid a collision of random access, thebase station B selects a signature from among the base-station managedsignatures except signature being used in the base station B and theother base stations. Then, after assigning C-RNTI to the mobile station200 for performing handover, the base station B notifies the basestation A of a handover request acknowledge command including thesignature number and C-RNTI as a response to the handover requestcommand (ST606).

Upon receiving the handover request acknowledge command from the basestation B, the base station A transmits a handover command including thesignature number and C-RNTI to the mobile station 200 (ST607). Further,the base station A transmits a handover notification command fornotifying that the signature of signature number 1 is used between thebase stations A and B to the base station C (ST608). When the handovernotification command arrives from the base station A, the base station Creceives the command (ST609), and registers that the signature ofsignature number 1 is used between the base stations A and B.

Upon receiving the handover command from the base station A, the mobilestation 200 acquires downlink synchronization with the base station B,and checks a position of the random access channel from the broadcastchannel (ST610). After acquiring downlink synchronization, the mobilestation 200 gains access to the base station B on the random accessusing a preamble (random access preamble) including a signature of thesignature number added to the handover command i.e. the signature ofsignature number 1 (ST611).

Upon detecting the signature from the preamble received from the mobilestation 200, the base station B determines whether the signature isassigned by the base station B (ST612). Herein, since the base station Breceives the signature of signature number 1 and this signature ofsignature number 1 is assigned by the base station B, the base station Bcalculates a synchronization timing deviation amount and performsscheduling for transmitting a handover completion message (ST613). Then,the base station B transmits the synchronization timing deviationinformation (synchronization information), scheduling information andC-RNTI (ST614). In this case, since C-RNTI is beforehand notified, thesignature number is not required as identification information forchecking data to the mobile station 200 by the station 200, and C-RNTIis enough.

In addition, in the determination in ST612, when the base station Bdetermines that the signature received from the mobile station 200 isnot the signature assigned by the base station B, the base station Bdoes not respond to the mobile station 200 to leave (ST615).

Upon receiving the information to the mobile station 200 from the basestation B, the station 200 corrects the synchronization timing deviationbased on the synchronization timing deviation information(synchronization information) (ST616). Then, the mobile station 200transmits a handover completion message with radio resources subjectedto scheduling (ST617). Upon receiving the handover completion messagefrom the mobile station 200, the base station B sends back a response tothe mobile station 200 in response to the message (ST618).

Thus, in the communication system according to Embodiment 3, since theinformation of signatures to use is shared among adjacent base stationsand selection of signatures is adjusted, it is possible to reducecollisions that could occur with the adjacent base station in randomaccess at the time of handover.

In addition, in the communication system according to Embodiment 3, asST608 as shown in FIG. 6, the case is indicated that the base station Atransmitting a handover request command transmits a handovernotification command to the adjacent base station C. However, the basestation transmitting a handover notification command is not limited tothe base station A transmitting a handover request command, and may bethe base station B receiving a handover request command. Also in thusmodified case, it is possible to obtain the same effect as in the casedescribed above.

Further, in the communication systems according to Embodiments 1 to 3,the case is shown that the base station 100 selects a signature, andnotifies the mobile station 200 of the signature using a handovercommand (handover message), but the information capable of beingnotified by the handover command is not limited thereto, and is capableof being modified as appropriate. For example, the base station mayselect not only the signature but also a frequency band position of therandom access channel to notify the mobile station with a handovermessage. In this case, it is possible to decrease the probability ofcollision at the time of random access by selection of a frequency bandposition of the random access channel, and it is thereby possible torespond to handovers concurrently arising in the higher number of mobilestations 200.

Furthermore, as well as the frequency band position of the random accesschannel as described above, a time position may be selected to benotified to the mobile station 200 with a handover message. In thiscase, it is possible to further reduce the probability of collision atthe time of random access, and it is thereby possible to respond tohandovers concurrently arising in the further higher number of mobilestations 200. However, when different ranges of signatures are allocatedfor each base station 100 i.e. signatures to use are different for eachbase station 100, it is not necessary to notify and adjust signaturesamong base stations 100, and it is only required to manage signatureswithin the base station 100.

Embodiment 4

In the communication systems according to Embodiments 1 to 3, withrespect to base-station managed signatures, the case is shown thathandover is set as their intended purpose. However, the intended purposeset on the base-station managed signatures is not limited thereto, andis capable of being modified as appropriate. In a communication systemaccording to Embodiment 4, with respect to the base-station managedsignatures, paging response is set as their intended purpose, as well ashandover.

In addition, configurations of the base station 100 and mobile station200 constituting the communication system according to Embodiment 4 arethe same as those in Embodiment 1, and descriptions thereof are omitted.Further, signatures in the communication system according to Embodiment4 differ from those in the communication system according to Embodiment1 in the respect that base-station managed signatures are set forhandover and paging response as their intended purposes.

FIG. 7 is a diagram to explain a setting example of signatures in thecommunication system according to Embodiment 4 of the invention. In thecommunication system according to Embodiment 4, as shown in FIG. 7,signature numbers 1 to 32 are allocated as base-station managedsignatures, and signature numbers 33 to 64 are allocated asmobile-station managed signatures. Among the base-station managedsignatures, signature numbers 1 to 16 are set for handover as theirintended purpose, and signature numbers 17 to 32 are set for pagingresponse as their intended purpose.

Described below is an example of a random access procedure at the timeof receiving paging in the communication system according to Embodiment4. FIG. 8 is a sequence chart to explain an example of a random accessprocedure at the time of receiving paging in the communication systemaccording to Embodiment 4.

As shown in FIG. 8, in the random access procedure at time of receivingpaging in the communication system according to Embodiment 4, an accessgateway AGW first transmits paging information to the base station 100(ST801).

Upon receiving the paging information from the access gateway AGW, thebase station 100 selects one signature from signatures for pagingresponse among the base-station managed signatures (ST802). Herein, asignature of signature number 17 is assumed to be selected. In thiscase, to avoid a collision of random access, the base station 100selects a signature from among the base-station managed signaturesexcept signatures for paging response being used in the base station100. Then, the base station 100 adds the selected signature number to apaging message to transmit to the mobile station 200 (ST803).

Upon receiving the paging message from the base station 100, the mobilestation 200 transmits a preamble (random access preamble) including asignature of the signature number added to the paging message i.e. thesignature of signature number 17 to the base station 100 on the randomaccess channel (ST804). Upon detecting the signature from the preamblereceived from the mobile station 200, the base station 100 determineswhether the signature is assigned by the base station 100 (ST805).Herein, since the base station 100 receives the signature of signaturenumber 17 and this signature of signature number 17 is assigned by thebase station 100, the base station 100 calculates a synchronizationtiming deviation amount and performs scheduling for transmitting anL2/L3 message (ST806). Further, the base station 100 selects C-RNTI, andtransmits the synchronization timing deviation information(synchronization information), scheduling information, C-RNTI and thesignature number to the mobile station 200 (ST807).

In addition, in the determination in ST805, when the base station 100determines that the signature received from the mobile station 200 isnot the signature assigned by the base station 100, the base station 100does not respond to the mobile station 200 to leave (ST808).

Upon receiving the information to the mobile station 200 from the basestation 100, the station 200 transmits an L2/L3 message with radioresources subjected to scheduling (ST809). Upon receiving the L2/L3message from the mobile station 200, the base station 100 sends back aresponse to the mobile station 200 in response to the message (ST810).

Thus, in the communication system according to Embodiment 4, since thebase-station managed signatures include signatures associated with aresponse at the time of receiving paging as the reason of random access,it is possible to prevent a collision from occurring in random access atthe time of responding to paging. As a result, it is possible to preventthe connection time from being long due to the collision.

Particularly, in the communication system according to Embodiment 4, asignature selected by the base station 100 is included in a pagingmessage and transmitted to the mobile station 200, and therefore, it ispossible to transmit the signature selected by the base station 100 tothe mobile station 200 exploiting an already-existing signal.

In addition, in the communication system according to Embodiment 4, thecase is shown that the base station 100 selects a signature, andnotifies the mobile station 200 of the signature using a paging message,but the information capable of being notified by the paging message isnot limited thereto, and is capable of being modified as appropriate.For example, the base station may select not only the signature but alsoa frequency band position of the random access channel to notify themobile station with a paging message. In this case, it is possible todecrease the probability of collision at the time of random access byselection of a frequency band position of the random access channel, andit is thereby possible to cope with paging responses concurrentlyarising in the higher number of mobile stations.

Further, as well as the frequency band position of the random accesschannel as described above, a time position may be selected to benotified to the mobile station with a paging message. In this case, itis possible to further reduce the probability of collision at the timeof random access, and it is thereby possible to cope with pagingresponses concurrently arising in the further higher number of mobilestations.

Furthermore, in the communication system according to Embodiment 4, asshown in FIG. 7, it is described that the base-station managedsignatures are divided into signatures for handover and signatures forpaging response according to their intended purposes. However, in thebase-station managed signatures, the base station 100 already recognizesthe purpose of random access of the mobile station 200, and therefore,it is not necessary that the base-station managed signatures are alwayssorted according to the purposes. Particularly, in the sense ofenlarging choices of the base-station managed signatures, it ispreferable that the signatures are not sorted according to the purposes.

Embodiment 5

In the communication systems according to Embodiments 1 to 4, the caseis shown that the range of base-station managed signatures and the rangeof mobile-station managed signatures are fixed. In contrast thereto, acommunication system according to Embodiment 5 differs from thecommunication systems according to Embodiments 1 to 4 in the respectthat respective ranges of the base-station managed signatures andmobile-station managed signatures are selectable corresponding toconditions of the base station 100.

FIG. 9 is a diagram to explain the summary of setting of signatures inthe communication system according to Embodiment 5 of the invention. Inthe communication system according to Embodiment 5, as shown in FIG. 9,in the case of the high number of mobile stations 200 communicating withthe base station 100, since random access due to handover and the likeis considered to increase, the number of base-station managed signaturesis increased. Meanwhile, in the case of the low number of mobilestations 200 communicating with the base station 100, since randomaccess due to handover and the like is considered to decrease, in orderto reduce the collision from the mobile stations, the number ofbase-station managed signatures is decreased, while the number ofmobile-station managed signatures is increased.

A setting example of signatures in the communication system according toEmbodiment 5 will specifically be descried below. FIG. 10 is a diagramshowing a table (hereinafter, referred to as a “number-of-signaturedetermination table) referred to in determining the numbers ofbase-station managed signatures and mobile-station managed signatures inthe communication system according to Embodiment 5. Further, FIG. 11 isa diagram to explain a setting example of signatures in thecommunication system according to Embodiment 5.

As shown in FIG. 10, in the number-of-signature determination table, thenumber (hereinafter, referred to as “the number of connected mobilestations”) of the mobile stations 200 with which the base station 100are communicating is associated with the signature group managementnumber, the number of base-station managed signatures, and the number ofmobile-station managed signatures. In FIG. 10, the case is shown thatthresholds of the number of connected mobile stations are A, B, C and D(assuming A<B<C<D) and thus four. In the base station 100, in responseto the number of connected mobile stations, the signature groupmanagement number is determined, thereby varying the number ofbase-station managed signatures and the number of mobile-station managedsignatures. In addition, common signatures are used between the basestation 100 and mobile stations 200.

FIG. 11( a) shows a setting example of signatures when the number ofconnected mobile stations is less than or equal to the lowest thresholdA. In FIG. 11( a), the case is shown where signature group managementnumber 1 is selected and the number of mobile-station managed signaturesis higher than the number of base-station managed signatures. FIG. 11(b) shows a setting example of signatures when the number of connectedmobile stations is between threshold B and threshold C. In FIG. 11( b),the case is shown where signature group management number 3 is selectedand the number of mobile-station managed signatures is equal to thenumber of base-station managed signatures. FIG. 11( c) shows a settingexample of signatures when the number of connected mobile stations ismore than or equal to the highest threshold D. In FIG. 11( c), the caseis shown where signature group management number 5 is selected and thenumber of mobile-station managed signatures is lower than the number ofbase-station managed signatures.

The base station 100 selects a signature from the signature groupmanagement number thus selected corresponding to the number of connectedmobile stations. Then, the base station 100 notifies the mobile station200 of the signature group management number through the broadcastinformation. The mobile station 200 selects a signature groupcorresponding to the signature group management number as in the basestation 100, and selects a signature from the selected signature group.Thus, since the signature group management number is included in thebroadcast information, it is possible to notify the mobile station 100of the signature group management number exploiting an already-existingsignal.

In addition, shown herein is the case that the numbers of base-stationmanaged signatures and mobile-station managed signatures are variedcorresponding to the number of connected mobile stations. However, thecriterion in varying the numbers of base-station managed signatures andmobile-station managed signatures is not limited thereto, and is capableof being modified as appropriate. For example, the usage rate of theuser data channel on downlink or uplink and the like may be used as thecriterion. Further, considering conditions of adjacent base stations 100is preferable as the Embodiment.

Described herein is an example of configurations of the base station 100and mobile station 200 included in the communication system according toEmbodiment 5. FIG. 12 is a block diagram showing an example of theconfiguration of the base station included in the communication systemaccording to Embodiment 5. FIG. 13 is a block diagram showing an exampleof the configuration of the mobile station included in the communicationsystem according to Embodiment 5. In addition, in FIGS. 12 and 13, thesame structural elements as in FIGS. 2 and 3 are assigned the samereference numerals, and descriptions thereof are omitted.

The base station 100 included in the communication system accordingEmbodiment 5 differs from the base station 100 according to Embodiment 1in respects that a signature group selecting section 1201 is provided,and that a signature selecting section 1202 and signature managingsection 1203 have different functions. Described below are the signaturegroup selecting section 1201, signature selecting section 1202 andsignature managing section 1203.

The signature group selecting section 1201 selects the base-stationmanaged signature group and mobile-station managed signature group basedon information of connection with the mobile station 200 from the higherlayer, and notifies the selection result to the signature selectingsection 1202 and signature managing section 1203. Further, to notify themobile station 200 of the information of the selected signature groupsthrough broadcast information, the signature group selecting section1201 outputs the selected signature group management number to the datacontrol section 101. The signature selecting section selects a signaturefrom the base-station managed signature group notified from thesignature group selecting section to notify the higher layer.

By directions from the higher layer, the signature selecting section1202 selects a signature from the base-station managed signature groupnotified from the signature group selecting section 1201 to notify thehigher layer and signature group managing section 1203. In selecting asignature, the signature selecting section 1202 checks with thesignature managing section 1203 for signature numbers being used, andselects one from among signatures except the signatures being used.

The signature managing section 1203 stores a signature number selectedin the signature selecting section 1202, and deletes the base-stationmanaged signature detected in the preamble detecting section 108 fromstored signatures.

Meanwhile, the mobile station 200 included in the communication systemaccording to Embodiment 5 differs from the mobile station 200 accordingto Embodiment 1 in respects that a control data extracting section 1301and signature selecting section 1302 have different functions, and thata signature group managing section 1303 is provided. Described below arethe control data extracting section 1301, signature selecting section1302 and signature group managing section 1303.

The control data extracting section 1301 divides reception data intouser data and control data. In the divided control data, schedulinginformation is output to the scheduling section 203, uplinksynchronization information is output to the synchronization correctingsection 206, the signature group management number is output to thesignature group managing section 1303, and the other control data anduser data is output to the higher layer. The signature group managingsection 1303 constructs a signature group from the signature groupmanagement number received from the control data extracting section1301, and outputs the resultant to the signature selecting section 1302.

The signature selecting section 1302 selects a signature number to usein random access by directions from the higher layer. As directions fromthe higher layer, the purpose of random access is notified. When thenotified purpose is a base-station managed purpose such as handover,paging or the like, the signature selecting section 1302 selects asignature number instructed from the higher layer. When the notifiedpurpose is a mobile-station managed purpose, the signature selectingsection 1302 randomly selects a signature number from signatures sortedaccording to the purpose among mobile-station managed signatures of thesignature group output from the signature group managing section 1303,corresponding to the purpose. The signature selecting section 1302outputs the selected signature number to the preamble generating section205.

Thus, in the communication system according to Embodiment 5, sincerespective ranges of the base-station managed signatures andmobile-station managed signatures are selectable corresponding toconditions of the base station 100, it is possible to select the optimalnumbers of base-station managed signatures and mobile-station managedsignatures corresponding to conditions of the base station 100, and toefficiently prevent the collision within the base station 100 due torandom access.

The present invention is not limited to the above-mentioned Embodiments,and is capable of being carried into practice with various modificationsthereof. In the above-mentioned Embodiments, sizes, shapes and the likeas shown in the accompanying drawings are not limited thereto, and arecapable of being modified as appropriate within the scope of exhibitingthe effects of the invention. Moreover, the invention is capable ofbeing carried into practice with modifications thereof as appropriatewithout departing from the scope of the object of the invention.

For example, in the above-mentioned Embodiments, as examples of thereason of random access associated with base-station managed signatures,handover and response at the time of receiving paging are shown, but theinvention is not limited thereto, and is capable of being modified asappropriate. For example, reasons such as synchronization maintenanceand the like may be associated as the reason of random access. In thiscase, it is possible to maintain synchronization under the imitative ofthe base station 100.

1-36. (canceled)
 37. A base station for handling random access by amobile station, wherein signatures used in the random access are formedof a first signature group selectable by the base station, and a secondsignature group selectable by the mobile station, and the base stationbroadcasts information enabling the second signature group to beidentified in the mobile station to the mobile station.
 38. The basestation according to claim 37, wherein when the base station selects asignature used in random access by the mobile station from the firstsignature group to assign to the mobile station, the base stationnotifies the mobile station of information enabling the signatureassigned to the mobile station to be identified in the mobile station.39. A mobile station for performing random access to a base station,wherein signatures used in the random access are formed of a firstsignature group selectable by the base station, and a second signaturegroup selectable by the mobile station, and the mobile station acquiresinformation enabling the second signature group to be identified frombroadcast information from the base station, identifies the secondsignature group according to the information enabling the secondsignature group to be identified, and performs random access to the basestation using a signature selected from the second signature group. 40.The mobile station according to claim 39, wherein when the mobilestation acquires information enabling identification of a signature thatthe base station assigns to the mobile station from the first signaturegroup, the mobile station identifies the signature assigned from theinformation, and performs random access using the signature.
 41. Acommunication system in which a base station handles random access by amobile station, wherein signatures used in the random access are formedof a first signature group selectable by the base station, and a secondsignature group selectable by the mobile station, the base stationbroadcasts information enabling the second signature group to beidentified in the mobile station to the mobile station, and the mobilestation identifies the second signature group from the information,acquired from the base station, enabling the second signature group tobe identified, and performs random access to the base station using asignature selected from the second signature group.
 42. Thecommunication system according to claim 41, wherein when the basestation selects a signature used in random access by the mobile stationfrom the first signature group to assign to the mobile station, the basestation notifies the mobile station of information enabling thesignature assigned to the mobile station to be identified, and themobile station identifies the signature assigned from the informationenabling the signature to be identified, and performs random accessusing the signature.
 43. A base station for handling random access by amobile station, wherein signatures used in the random access are formedof a first signature group selectable by the base station, and a secondsignature group selectable by the mobile station, and the base stationis capable of performing control for varying the number of signaturescontained in the first signature group and the number of signaturescontained in the second signature group.
 44. The base station accordingto claim 43, wherein the base station performs control for increasingone of the number of signatures contained in the first signature groupand the number of signatures contained in the second signature group,while decreasing the other number.
 45. The base station according toclaim 43, wherein the base station broadcasts information enabling thesecond signature group to be identified to the mobile station.
 46. Thebase station according to claim 44, wherein the base station broadcastsinformation enabling the second signature group to be identified to themobile station.
 47. The base station according to claim 43, wherein whenthe base station selects a signature used in random access by the mobilestation from the first signature group to assign to the mobile station,the base station notifies the mobile station of information enabling thesignature assigned to the mobile station to be identified in the mobilestation.
 48. A communication system in which a base station handlesrandom access by a mobile station, wherein signatures used in the randomaccess are formed of a first signature group selectable by the basestation, and a second signature group selectable by the mobile station,the base station is capable of performing control for varying the numberof signatures contained in the first signature group and the number ofsignatures contained in the second signature group, and broadcastsinformation enabling the second signature group to be identified in themobile station to the mobile station, and the mobile station identifiesthe second signature group according to the information, acquired fromthe base station, enabling the second signature group to be identified,and performs random access to the base station using a signatureselected from the second signature group.
 49. The communication systemaccording to claim 48, wherein the base station performs control forincreasing one of the number of signatures contained in the firstsignature group and the number of signatures contained in the secondsignature group, while decreasing the other number.
 50. Thecommunication system according to claim 48, wherein when the basestation selects a signature used in random access by the mobile stationfrom the first signature group to assign to the mobile station, the basestation notifies the mobile station of information enabling thesignature assigned to the mobile station to be identified, and themobile station identifies the signature assigned from the informationenabling the signature to be identified, and performs random accessusing the signature.
 51. The communication system according to claim 49,wherein when the base station selects a signature used in random accessby the mobile station from the first signature group to assign to themobile station, the base station notifies the mobile station ofinformation enabling the signature assigned to the mobile station to beidentified, and the mobile station identifies the signature assignedfrom the information enabling the signature to be identified, andperforms random access using the signature.